Connecting system for plastic columns

ABSTRACT

The invention relates to a plastic cartridge system essentially comprising a cartridge consisting of a plastic-covered column, said column comprising a monolithic sorbent and at least one closing cap which is applied to the ends of the column. The cartridge also consists of a connecting system comprising at least one divided supporting screw which is held in position by a closing cap or a spacer ring, and at least one end piece which can be screwed onto a supporting screw in order to connect an elution agent inlet and an elution agent outlet.

[0001] The invention relates to a cartridge system which is especiallymatched to the properties of plastic-clad monolithic chromatographycolumns.

[0002] Columns for chromatography, in particular for HPLC, usually havea cladding of metal or plastic into which the sorbent has beenintroduced. Besides conventional particulate sorbents, monolithicsorbents, as disclosed, for example, in WO 94/19687 and in WO 95/03256,are also gaining increased importance.

[0003] In order to produce columns with particulate sorbents, columntubes, typically of metal or plastic, are sealed at one end with afilter system and filled with the sorbent under pressure. During thisoperation, it is ensured that the sorbent particles fill the entire tubein order that no dead space is formed which could impair the separationefficiency. After filling, the column is sealed at both ends withintegrated or attached filter systems in order that sorbent cannotescape during use. The connection to eluent feed and discharge takesplace through screw connections, which are screwed directly onto thecolumn (for plastic or metal columns) or via re-usable cartridge systemswhich are inserted into the columns (for metal columns).

[0004] In contrast to particulate sorbents, which can be introduced intoprefabricated metal columns, some peculiarities have to be taken intoaccount in the cladding and connection of monolithic sorbents:

[0005] Monolithic sorbents are generally removed from the mould afterproduction and re-clad for use. Since monolithic sorbents have a rigidshape and dead spaces arising during the cladding cannot be compensatedfor, the cladding of the monoliths must be carried out with no deadspace and in a pressure-stable manner. It has been found that plasticcladding is particularly suitable since it has adequate pressurestability and can be applied to the monolithic sorbent with no deadspace. The sorbent generally terminates flush with the cladding at theends.

[0006] Monolithic columns have hitherto been connected to the eluentfeed or outlet via screw connections, which are screwed directly onto athread cut into the plastic cladding. If the screw connection isremoved, the monolithic sorbent is directly accessible and can easily bedamaged. A connecting system for monolithic plastic-clad sorbents in theform of a cartridge system was hitherto unknown. Owing to the materialproperties of sorbent and cladding, the metal cartridge systems knownfor particulate sorbents cannot be applied to monolithic plastic-cladsorbents. In particular, different demands are made of columntermination elements, such as, for example, filter elements.

[0007] The object of the present invention was therefore to develop aconnecting system for plastic-clad monolithic sorbents which enables useas a cartridge system.

[0008] It has been found that a cartridge system consisting of a columnwith cap which is installed directly on the ends of the cladding, aspacer ring for integration of a pre-column, a divided supporting screwand an end piece which can be screwed onto the supporting screw for theconnection of eluent feed and discharge meets all requirements of aconnecting system for columns comprising plastic-clad monolithicsorbents.

[0009] The present invention therefore relates to a cartridge system atleast comprising

[0010] a cartridge consisting of a plastic-clad column with monolithicsorbent on which a cap is installed at least at one end, p1 and aplastic connecting system consisting of at least one divided supportingscrew and at least one end piece which is screwed onto the saidsupporting screw for the connection of eluent feed and discharge.

[0011] In a preferred embodiment, a device is present which enables thesupporting screw to be placed against the cartridge at at least twodifferent defined points. This device can be, for example, at least onespacer ring or a shape (for example recess or bead) provided for thispurpose in the cap.

[0012] In a particularly preferred embodiment, the device is at leastone spacer ring.

[0013] In a preferred embodiment, the cartridge cap has an internalthread for screwing onto the column.

[0014] The present invention also relates to the use of the cartridgesystem according to the invention for the chromatographic separation ofat least two substances.

[0015]FIG. 1 shows a cartridge system according to the invention havinga cartridge and the connecting system.

[0016] The cartridge system according to the invention consists of acartridge, which in turn consists at least of a column with cap and aconnecting system. The cartridge system is suitable for plastic-cladcolumns with monolithic sorbents, irrespective of the nature of thesorbent or of the plastic. The columns are preferably those withinorganic monolithic sorbents which are clad with thermoplastics, suchas, for example, polyaryls, polyether ketones, polyesters, aromaticpolyamides, polyimides, polybenzimidazoles, preferably fluorinatedpolymers, polyphenylene sulfides, polyether sulfones orliquid-crystalline polymers (LCPs) and mixtures of two or more of thesematerials. If the plastics do not exhibit adequate pressure stability orare difficult to process, they may have been treated with stabilisers,such as fibre materials, inorganic materials, or pigments, for examplechalk, talc, mica or inorganic oxides, such as silicon dioxide. Thecartridge system according to the invention is particularly suitable forcolumns comprising fibre-reinforced plastics, especially comprisingglass or in particular carbon fibre-reinforced PEEK (polyether etherketone). The other constituents of the cartridge system, such as thecap, supporting screw and end pieces, likewise preferably consist ofplastic, where the same materials can generally be employed as are alsoused for the cladding. It is also possible to employ fibre-reinforcedplastics for these parts, since they have greater mechanical stability.However, non-fibre-reinforced plastics are usually also sufficientlystable for parts such as the cap, spacer ring, supporting screw and endpiece.

[0017] For protection of the monolithic sorbent and for homogeneousdistribution of the eluent on the sorbent, the column is firstlyprovided, in accordance with the invention, with a cap. This cap can bepermanently or reversibly connected to the column, i.e. it can beattached, for example, by screwing, adhesive bonding, clamping orwelding. It has been found that the attachment known for metal columnsvia a groove into which two half-shells can be inserted (for exampledisclosed in EP 0268185) cannot be used in the case of plastic columns.The plastic material is destabilised to a very considerable extent bycutting-in of a groove and thus loses the requisite pressure stability.The cap is preferably attached by screwing onto a thread locateddirectly on the cladding. This offers the possibility of integratingeven columns which are provided with a conventional screwed-onconnecting system into the cartridge system according to the invention.

[0018] In columns for the cartridge system according to the invention,the monolithic sorbent preferably terminates flush with the cladding. Inthis case, the cap serves as sorbent protection. It furthermore containsa passage through which eluent can reach the column. This passagetypically consists of a distribution system, such as a perforated plate,a frit or a filter, which ensures uniform distribution of the eluent onthe sorbent, and a sealing element, which prevents the occurrence ofdead spaces or the escape of eluent at the side.

[0019] If the sorbent does not terminate flush with the cladding, butinstead a distribution element is already integrated into the columncladding at the ends, it is not necessary for a second distributionelement to be integrated into the cap. In this case, a liquid passage issufficient. Furthermore, it must be ensured that any dead spaces arecompensated for by correspondingly shaped sealing elements.

[0020] The cap can consist of a workpiece with integrated passage, etc.,or can be composed of a plurality of parts. For example, the cap canhave a passage into which a distribution unit is inserted.

[0021] A divided supporting screw is attached to the cap according tothe invention. The position of the supporting screw is determined by theshape and dimensions of the cap and any device provided for thispurpose. An end piece with connection for eluent feed and discharge isthen screwed onto the thread of the divided supporting screw. The endpiece can consist of one or more parts. The construction of end piecesis known to the person skilled in the art from other connecting systems.In general, it has, for the connection of eluent feed and discharge, aninternal thread into which a capillary or line can be screwed.

[0022] In order to enable integration of a pre-column, the position ofthe end piece must be variable in such a way that on the one hand apre-column can be inserted between the cap and end piece and on theother hand the end piece can be joined to the cap directly in anaccurately fitting manner. Since the position of the cap cannot bechanged, this is achieved in accordance with the invention by slidingthe supporting screw.

[0023] In one embodiment, the cap is shaped in such a way that thesupporting screw can be placed in two different positions. For example,the cap can have a device intended for this purpose in the form of oneor two grooves. The corresponding supporting screw has on the inside,for example, a raised ring, which can be placed against the end of thecap or against a groove. If a pre-column is to be integrated, the groovelocated closer to the column end is selected, so that the supportingscrew projects beyond the end of the column and a pre-column can beinstalled. If no pre-column is provided, the supporting screw is placedagainst the rear groove or against the end of the cap, so that the endpiece can be screwed on in an accurately fitting manner.

[0024] In a preferred embodiment, the cap does not have grooves.Instead, at least one loose spacer ring which surrounds the columnjacket and can be moved freely thereon between the caps at the ends ofthe column is located beneath the cap as device for positioning thesupporting screw. If integration of a pre-column is not intended, thespacer ring is moved right up against the cap. The supporting screw hason the inside a raised ring, a shoulder or another stop means. This isplaced against the spacer ring so that the supporting screw ispositioned in such a way that the end piece is positioned against thecap in an accurately fitting manner. For integration of a pre-column,the spacer ring is slid away from the cap, so that the supporting screwis located directly against the cap. This creates space for theinstallation of a pre-column. In accordance with the invention,provision may be made for one spacer ring, which is positioned in eachcase against the cap to which a pre-column is to be connected, twospacer rings, i.e. one for each side, or alternatively a plurality ofspacer rings of various thickness for the installation of pre-columns ofvarious length.

[0025] In a further embodiment, the spacer ring is shaped in such a waythat it can be joined to the cap in two ways. If a pre-column is notrequired, the spacer ring is joined to the cap in such a way that acavity is not created between the cap and end piece on attachment of thesupporting screw. For installation of a pre-column, the position of thespacer ring is changed in such a way that a cavity is created. Forexample, the spacer ring is in this embodiment designed in such a waythat it has at least two cut-outs in the length of the pre-column, i.e.,for example, a toothed end, on the side facing towards the cap. The capis correspondingly shaped in such a way that the spacer ring can beinstalled either with the outer edge or, through rotation, snaps intothe cut-outs and can thus be moved closer to the cap.

[0026]FIG. 1 shows a cartridge system according to the invention havinga cartridge in a connecting system. At the upper end, all parts of thesystem are attached to the column or cartridge; in the lower part, theyare, for better clarity, shown coordinated loosely to the column. Thecap (3) consists of two parts, a threaded part (3 a) with passage, whichis screwed onto the column, consisting of sorbent (1) and cladding (2).A distribution element (3 b) is placed against the threaded part. Thespacer ring (4) is connected to the cap (3) via a locking mechanism,such as, for example, a snap-in mechanism. If it is not required, thelock can be released and the spacer ring slid away to the column centre.For use without pre-column, as shown in FIG. 1, the divided supportingscrew (5 a, 5 b) is placed against the spacer ring (4). This is carriedout via a shoulder provided in the lower part of the supporting screw.For connection of eluent feed and discharge, the end piece (6) isscrewed onto the supporting screw (5 a, 5 b). The end piece (6) consistsof two parts, the connector (6 a) and a union nut (6 b).

[0027] The cartridge system according to the invention thus offers asimple system for the connection of plastic columns with monolithicsorbents. The cap means that it is not necessary to integrate a filterunit directly into the column. Protection of the monolithic sorbentagainst damage and uniform feed of the eluent onto the sorbent areprovided by the cap. The attachment of the cap is matched to the plasticcladding.

[0028] The connection between end piece and cap is provided via adivided supporting screw. Metal screws which have been cut and laterdivided give rise to the problem that the thread only functions reliablyif the screw parts originally belonging together are used together. Thisis unsuitable for mass production. In the case of divided screws madefrom plastic, this problem does not exist if they are made, inaccordance with the invention, as two defined parts, preferably by meansof injection moulding. In this way, exchangeability of the thread halvesis ensured.

[0029] Since the cap is preferably screwed onto the column, means mustbe provided, for integration of a pre-column, for positioning of thesupporting screw in at least two possible positions. This is facilitatedin accordance with the invention by a device provided for this purpose,preferably by a spacer ring.

[0030] The system according to the invention can be utilised ascartridge system by, for example, using the column with caps and, ifdesired, with spacer ring as a replaceable cartridge.

[0031] In general, a column for chromatographic operation is provided atboth ends with the cap and the connections according to the invention.

[0032] Even without further details, it is assumed that a person skilledin the art will be able to utilise the above description in its broadestscope. The preferred embodiments and examples should therefore merely beregarded as descriptive disclosure which is absolutely not limiting inany way.

[0033] The complete disclosure content of all applications, patents andpublications mentioned above and below, in particular of thecorresponding application DE 100 34 076, filed on Jul. 13, 2000, isincorporated into this application by way of reference.

1. Cartridge system at least comprising a cartridge consisting of aplastic-clad column with monolithic sorbent on which a cap is installedat least at one end, and a plastic connecting system consisting of atleast one divided supporting screw and at least one end piece which isscrewed onto the said supporting screw for the connection of eluent feedand discharge.
 2. Cartridge system according to claim 1, furthermorecharacterised in that a device is present which enables the supportingscrew to be placed against the cartridge at at least two differentpoints.
 3. Cartridge system according to claim 2, characterised in thatthe device is at least one spacer ring.
 4. Cartridge system according toone of claims 1 to 3, furthermore characterised in that the cartridgecap has an internal thread for screwing onto the column.
 5. Use of acartridge system according to one of claims 1 to 4 for thechromatographic separation of at least two substances.